arXiv subjects

L. Iliev

Publications and source records attributed to L. Iliev.

6 recordsLinked to original sources

arXiv2024

Investigation of the Nature of the B[e] Star CI Cam in the Optical Range

We report the results of 24 years of photometric and spectroscopic monitoring of CI Cam since its outburst in 1998. In the early years of our research, we identified a system component responsible for the emission of the He II 4686 line, which moves in an elliptical orbit with a period of 19.407 days and an eccentricity from 0.44 to 0.49. Variations in optical brightness with the same period were observed, with an average amplitude of 0.04 magnitudes. The total amplitude of the He II radial velocity variations was approximately 380 kilometers per second. The equivalent width of the line varied on timescales of tens of minutes as well as with the orbital period, reaching maximum values when the companion passed the descending node of the orbit. The intensity of the He II 4686 emission has gradually increased over time. Our photometric monitoring revealed pulsations of the main B component of the CI Cam system. Between 2005 and 2009, the B star exhibited multiperiodic pulsations, however, since 2012, it pulsated in a single mode. We interpret the pulsations from 2005 to 2009 as a resonance of radial modes, with the residual stable mode being the first overtone. The pulsations are coherent over several months, with average amplitudes from 0.02 to 0.04 magnitudes in the V band. The pulsation data constrain the spectral type of the primary component of B0 to B2 III, the distance to the system from 2.5 to 4.5 kpc. The classification of the main component of CI Cam as a supergiant is ruled out due to the observed pulsation periods. CI Cam is likely in the stage after the first mass exchange and may belong to the FS CMa-type objects.

astro-ph.SR↗

arXiv2020

An eccentric wave in the circumstellar disc of the Be/X-ray binary X Persei

We present spectroscopic observations of the Be/X-ray binary X Per obtained during the period December 2017 - January 2020 (MJD~58095 - MJD~58865). In December 2017 the $Hα$, $Hβ$, and HeI 6678 emission lines were symmetric with violet-to-red peak ratio $V/R \approx 1$. During the first part of the period (December 2017 - August 2018) the V/R-ratio decreased to 0.5 and the asymmetry developed simultaneously in all three lines. In September 2018, a third component with velocity $\approx 250$~km~s$^{-1}$ appeared on the red side of the HeI line profile. Later this component emerged in $Hβ$, accompanied by the appearance of a red shoulder in $Hα$. Assuming that it is due to an eccentric wave in the circumstellar disc, we find that the eccentric wave appeared first in the innermost part of the disc, it spreads out with outflowing velocity $v_{wave} \approx 1.1 \pm 0.2 $~km~s$^{-1}$, and the eccentricity of the eccentric wave is $e_{wave} \approx 0.29 \pm 0.07$. A detailed understanding of the origin of such eccentricities would have applications to a wide range of systems from planetary rings to AGNs.

astro-ph.SR↗

arXiv2011

On the nature of the Be star HR 7409 (7 Vul)

HR 7409 (7 Vul) is a newly identified Be star possibly part of the Gould Belt and is the massive component of a 69-day spectroscopic binary. The binary parameters and properties of the Be star measured using high-dispersion spectra obtained at Ondrejov Observatory and at Rozhen Observatory imply the presence of a low mass companion (~ 0.5-0.8 M_sun). If the pair is relatively young (<50-80 Myr), then the companion is a K V star, but, following another, older evolutionary scenario, the companion is a horizontal-branch star or possibly a white dwarf star. In the latter scenario, a past episode of mass transfer from an evolved star onto a less massive dwarf star would be responsible for the peculiar nature of the present-day, fast-rotating Be star.

astro-ph.SR↗

arXiv2010

Spectroscopic analysis of the B/Be visual binary HR 1847

We studied both components of a slightly overlooked visual binary HR 1847 spectroscopically to determine its basic physical and orbital parameters. Basic stellar parameters were determined by comparing synthetic spectra to the observed echelle spectra, which cover both the optical and near-IR regions. New observations of this system used the Ondřejov and Rozhen 2-m telescopes and their coudé spectrographs. Radial velocities from individual spectra were measured and then analysed with the code {\FOTEL} to determine orbital parameters. The spectroscopic orbit of HR 1847A is presented for the first time. It is a single-lined spectroscopic binary with a B-type primary, a period of 719.79 days, and a highly eccentric orbit with e=0.7. We confirmed that HR 1847B is a Be star. Its Hαemission significantly decreased from 2003 to 2008. Both components have a spectral type B7-8 and luminosity class IV-V.

astro-ph.SR↗

arXiv2010

Properties and nature of Be stars: 27. Orbital and recent long-term variations of the Pleiades Be star Pleione = BU Tauri

Radial-velocity variations of the H-alpha emission measured on the steep wings of the H-alpha line, prewhitened for the long-time changes, vary periodically with a period of (218.025 +/- 0.022)d, confirming the suspected binary nature of the bright Be star Pleione, a member of the Pleiades cluster. The orbit seems to have a high eccentricity over 0.7, but we also briefly discuss the possibility that the true orbit is circular and that the eccentricity is spurious owing to the phase-dependent effects of the circumstellar matter. The projected angular separation of the spectroscopic orbit is large enough to allow the detection of the binary with large optical interferometers, provided the magnitude difference primary - secondary is not too large. Since our data cover the onset of a new shell phase up to development of a metallic shell spectrum, we also briefly discuss the recent long-term changes. We confirm the formation of a new envelope, coexisting with the previous one, at the onset of the new shell phase. We find that the full width at half maximum of the H-alpha profile has been decreasing with time for both envelopes. In this connection, we briefly discuss Hirata's hypothesis of precessing gaseous disk and possible alternative scenarios of the observed long-term changes.

astro-ph.SR↗

arXiv2002

The radial velocities and physical parameters of HD 553

HD 553 was discovered as an eclipsing binary by Hipparcos. Here, we present the first radial velocity curve for this system. It is found that HD 553 is a double-lined spectroscopic binary. Despite the large luminosity difference, the two components of the system are of very simmilar mass. The primary, a K0-giant, fills a large fraction of its Roche-lobe. The secondary is, despite its very similar mass, still a late-type dwarf. The radial velocity curve allows to constrain several stellar and system parameters.

astro-ph↗